Best encryption method for USB for daily use

I use my USB daily and want to have something that will provide privacy, especially if I was to lose it. It will be backed up regularly onto my PC, but in the case of dropping it somewhere or forgetting it by accident, I don't want anyone accessing the data.

This means that whatever encryption I use I would ideally like it to be a fairly quick process. For example plug in, put password in, make changes if required/drop files …

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